[Haskell-cafe] type checking that I can't figure out ...

Vasili I. Galchin vigalchin at gmail.com
Wed Jun 3 13:18:28 EDT 2009

Hi Andrew (Bromage),

       I reversed the  parameter order to Data.Map.lookup and calling
fromJust to pull out value from Maybe wrapper ... all as you suggested:

> remLookupFwd :: (ReVars m t) => SimplRe t -> ReM m t (ReInfo t)
> remLookupFwd re
>   = do fwd <- gets resFwdMap
>        let { Just reinfo = fromJust(M.lookup re fwd) }
>        return reinfo

I am still getting a type mismatch:

    Couldn't match expected type `Maybe t'
           against inferred type `ReInfo t1'
    In the expression: fromJust (M.lookup re fwd)
    In a pattern binding: Just reinfo = fromJust (M.lookup re fwd)
    In the expression:
        do fwd <- gets resFwdMap
           let Just reinfo = fromJust (M.lookup re fwd)
           return reinfo

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